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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Naphthalene‐Diimide‐Based Ionenes as Universal Interlayers for Efficient Organic Solar Cells

Abstract Self‐doping ionene polymers were efficiently synthesized by reacting functional naphthalene diimide (NDI) with 1,3‐dibromopropane ( NDI‐NI ) or trans ‐1,4‐dibromo‐2‐butene ( NDI‐CI ) via quaternization polymerization. These NDI‐based ionene polymers are universal interlayers with random molecular orientation, boosting the efficiencies of fullerene‐based, non‐fullerene‐based, and ternary organic solar cells (OSCs) over a wide range of interlayer thicknesses, with a maximum efficiency of 16.9 %. NDI‐NI showed a higher interfacial dipole (Δ), conductivity, and electron mobility than NDI‐CI , affording solar cells with higher efficiencies. These polymers proved to efficiently lower the work function ( WF ) of air‐stable metals and optimize the contact between metal electrode and organic semiconductor, highlighting their power to overcome energy barriers of electron injection and extraction processes for efficient organic electronics.

Liu, Ming↗
DOE OSTI2022

Estimating the energy requirement for hydrogen production in proton exchange membrane electrolysis cells using rapid operando hydrogen crossover analysis

Hydrogen (H 2 ) crossover in proton exchange membrane water electrolyzers refers to the process by which hydrogen produced at the cathode traverses the membrane and mixes with the oxygen produced at the anode. This phenomenon reduces efficiency and may pose flammability hazards. In this work we present a method for quantifying the H 2 content of the anode exhaust gas using a gas chromatograph that is capable of sampling data every 2 min. Subsequent theory is presented to calculate the crossover flux, overall H 2 efficiency, and H 2 energy requirements. Results the effects of membrane thickness using Nafion TM N117 (178 um) and Nafion TM NR212 (51 um) membranes. Furthermore, it was found that thinner membranes lead to improved VI performance but exhibit higher crossover rates. Despite their increased crossover, leading to decreased hydrogen efficiency, the calculated required energy for NR212 membrane-electrode assemblies (MEAs) was significantly lower than that of N117 MEAs.

08 HYDROGEN↗
DOE OSTI2023

Ultrathin Amorphous Gallium Oxide Vacuum Ultraviolet Photodetectors

Gallium oxide is demonstrated to be an effective material for the detection of vacuum-ultraviolet (VUV) photons. Nanometer thick films of amorphous gallium oxide deposited by atomic layer deposition are found to exhibit large absorptivity in the VUV region 120–200 nm. We leverage the strong absorption of the ultrathin film to fabricate self-powered Schottky diode photodetectors using graphene as a VUV-transparent electrode. In conclusion, responsivity throughout the VUV is calculated, significantly extending the demonstrated spectral range of gallium oxide-based photodetectors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Quincke Oscillations of Colloids at Planar Electrodes

Dielectric particles in weakly conducting fluids rotate spontaneously when subject to strong electric fields. Such Quincke rotation near a plane electrode leads to particle translation that enables physical models of active matter. In this Letter, we show that Quincke rollers can also exhibit oscillatory dynamics, whereby particles move back and forth about a fixed location. We explain how oscillations arise for micron-scale particles commensurate with the thickness of a field-induced boundary layer in the nonpolar electrolyte. This work enables the design of colloidal oscillators.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Correlating aluminum layer deposition rates, Josephson junction microstructure, and superconducting qubits’ performance

An ultra-thin aluminum oxide layer is a key component for Josephson junctions (JJ) in superconducting quantum bits (qubits). This layer serves as a barrier layer for Cooper pairs tunneling between the superconducting electrodes and significantly influences the overall performance of the junction. In this study, we investigate the impact of aluminum deposition rates on the microstructure and chemical variation of the aluminum oxide layer, as well as the device's yields and qubits’ lifetimes. Surprisingly, although the oxide layer roughness and thickness variation improve noticeably with an increasing Al deposition rate from 0.5 Å/s to 5 Å/s, the qubit's coherence time is almost unchanged. We attribute this to the fact that Cooper pairs tunnel only through the thinnest region of the barrier. Additionally, we revealed a stress-induced grain boundary sliding short-circuit failure mechanism in the JJ. Our discovery provides a vital understanding of oxide microstructure and JJ functionality, which are critical for improving the coherence time of superconducting qubits.

Coherence time↗
DOE OSTI2025

Ferroelectrically switched valley-dependent transmission in SnTe-PbTe-SnTe monolayer lateral heterostructures

A special class of valleytronic two-dimensional (2D) semiconductors possesses carrier pockets (i.e., valleys) along certain directions in the first Brillouin zone, which can be applied as a new degree of freedom for information storage and processing. Here we show that members of this family that are ferroelectric allow the location of these valleys to be switched by rotating the ferroelectric polarization. This makes possible the control of electronic state transmission probability through an energy barrier by ferroelectrically switching the polarization direction, thereby creating or eliminating valley matching in reciprocal space. We apply molecular beam epitaxy to grow lateral sandwich heterostructures with monolayer-thick ferroelectric SnTe separated by nanometer-wide paraelectric PbTe as the barriers. Using scanning tunneling microscopy, we show that the transmission probability of the 2D hole states at the valence band maximum of SnTe monolayer strongly relies on the relative orientation between the polarization directions of the two SnTe electrodes. The transmission can be switched from a suppressed state to a permitted state by rotating the ferroelectric polarization of one SnTe electrode by 90 degrees. Our work demonstrates the electric-field-control of valley locations and its potential for tunnel junction valleytronic devices.

electronic devices↗
NASA NTRS1993

On-line process analysis innovation: DiComp (tm) shunting dielectric sensor technology

The DiComp Shunting Dielectric Sensor (SDS) is a new patent-pending technology developed under the Small Business Innovation Research Program (SBIR) for NASA's Kennedy Space Center. The incorporation of a shunt electrode into a conventional fringing field dielectric sensor makes the SDS uniquely sensitive to changes in material dielectric properties in the KHz to MHz range which were previously detectable only at GHz measurement frequencies. The initial NASA application of the SDS for Nutrient Delivery Control has demonstrated SDS capabilities for thickness and concentration measurement of Hoagland nutrient solutions. The commercial introduction of DiComp SDS technology for concentration and percent solids measurements in dispersions, emulsions and solutions represents a new technology for process measurements for liquids in a variety of industries.

Davis, Craig R.↗
DOE OSTI2025

Inhomogeneous Magnetic Anisotropy in an Fe 5– x GeTe 2 Nanoflake Observed by Imaging

Few-layer flakes of ferromagnetic Fe 5–x GeTe 2 with x = 0.3 (F5GT) possess a c-axis magnetocrystalline anisotropy that is large enough below ∼200 K to outcompete the easy-plane shape anisotropy, yielding distinctive magnetic microstructures with out-of-plane (OOP) magnetizations. Using photoemission electron microscopy (PEEM) with magnetic contrast from X-ray magnetic circular dichroism (XMCD) to study a thermally demagnetized h-BN-protected nanoflake of F5GT at 110 K, we observe a micron-scale coexistence between domains with OOP magnetizations (∼70% areal fraction) and hitherto unknown domains in which in-plane (IP) magnetization components dominate (∼30% areal fraction). The regions with dominant IP magnetization components do not correlate with small variations of flake thickness (6–10 nm) and instead arise from local changes of magnetocrystalline anisotropy due to a hitherto unidentified chemical inhomogeneity that we suggest to be a higher concentration of Fe vacancies. Our observation of micron-scale inhomogeneity would likely be missed if imaging a single flake orientation and should affect the viability and performance of van der Waals (vdW) spintronic devices with F5GT electrodes.

2D materials↗
DOE OSTI2022

Scalable Gas Diffusion Electrode Fabrication for Electrochemical CO 2 Reduction Using Physical Vapor Deposition Methods

Electrochemical CO 2 reduction (ECR) promises the replacement of fossil fuels as the source of feedstock chemicals and seasonal storage of renewable energy. While much progress has been made in catalyst development and electrochemical reactor design, few studies have addressed the effect of catalyst integration on device performance. Using a microfluidic gas diffusion electrolyzer, we systematically studied the effect of thickness and the morphology of electron beam (EB) and magnetron-sputtered (MS) Cu catalyst coatings on ECR performance. We observed that EB-Cu outperforms MS-Cu in current density, selectivity, and energy efficiency, with 400 nm thick catalyst coatings performing the best. Additionally, the superior performance of EB-Cu catalysts is assigned to their faceted surface morphology and sharper Cu/gas diffusion layer interface, which increases their hydrophobicity. Tests in a large-scale zero-gap electrolyzer yielded similar product selectivity distributions with an ethylene Faradaic efficiency of 39% at 200 mA/cm 2 , demonstrating the scalability for industrial ECR applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A feasible path for the use of ferromagnetic josephson junctions in quantum circuits: The ferro-transmon

We discuss the capabilities of ferromagnetic (F) Josephson junctions (JJs) in a variety of layouts and configurations. The main goal is to demonstrate the potential of these hybrid JJs to disclose new physics and the possibility to integrate them in superconducting classical and quantum electronics for various applications. The feasible path towards the use of ferromagnetic Josephson junctions in quantum circuits starts from experiments demonstrating macroscopic quantum tunneling in NbN/GdN/NbN junctions with ferro-insulator barriers and with triplet components of the supercurrent, supported by a self-consistent electrodynamic characterization as a function of the barrier thickness. This has inspired further studies on tunnel ferromagnetic junctions with a different layout and promoted the first generation of ferromagnetic Al-based JJs, specifically Al/AlO x /Al/Py/Al. This layout takes advantage of the capability to integrate the ferromagnetic layer in the junction without affecting the quality of the superconducting electrodes and of the tunnel barrier. The high quality of the devices paves the way for the possible implementation of Al tunnel-ferromagnetic JJs in superconducting quantum circuits. These achievements have promoted the notion of a novel type of qubit incorporating ferromagnetic JJs. This qubit is based on a transmon design featuring a tunnel JJ in parallel with a ferromagnetic JJ inside a SQUID loop capacitively coupled to a superconducting readout resonator. In conclusion, the effect of an external RF field on the magnetic switching processes of ferromagnetic JJs has been also investigated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Covalent Functionalization of Silicon with Plasma-Grown “Fuzzy” Graphene: Robust Aqueous Photoelectrodes for CO 2 Reduction by Molecular Catalysts

Carbon electrodes are ideal for electrochemistry with molecular catalysts, exhibiting facile charge transfer and good stability. Yet for solar-driven catalysis with semiconductor light absorbers, stable semiconductor/carbon interfaces can be difficult to achieve, and carbon’s high optical extinction means it can only be used in ultrathin layers. Here, we demonstrate a plasma-enhanced chemical vapor deposition process that achieves well-controlled deposition of out-of-plane “fuzzy” graphene (FG) on thermally oxidized Si substrates. The resulting Si|FG interfaces possess a silicon oxycarbide (SiOC) interfacial layer, implying covalent bonding between Si and the FG film that is consistent with the mechanical robustness observed from the films. The FG layer is uniform and tunable in thickness and optical transparency by deposition time. Using p-type Si|FG substrates, noncovalent immobilization of cobalt phthalocyanine (CoPc) molecular catalysts was employed for the photoelectrochemical reduction of CO 2 in aqueous solution. The Si|FG|CoPc photocathodes exhibited good catalytic activity, yielding a current density of ∼1 mA/cm 2 , Faradaic efficiency for CO of ∼70% (balance H 2 ), and stable photocurrent for at least 30 h at −1.5 V vs Ag/AgCl under 1-sun illumination. Furthermore, the results suggest that plasma-deposited FG is a robust carbon electrode for molecular catalysts and suitable for further development of aqueous-stable Si photocathodes for CO 2 reduction.

CO2 reduction↗
DOE OSTI2025

Delineating Confinement Regimes for Nafion Thin Films via Simultaneous QCM-D and Spectroscopic Ellipsometry

Proton-conducting ionomers used in electrodes of electrochemical devices form nanometer-scale films covering metallic catalyst surfaces, wherein they experience confinement and interfacial effects absent in the bulk polymer. This confinement alters the physical properties of the ionomer film, which is postulated to increase the density and is attributed to the transport limitations observed in fuel-cell electrodes. Despite studies showing reduced swelling, no systematic measurement has validated this phenomenon by demonstrating both densification and stiffening as the film gets thinner. Here, this study aims to fill this gap by reporting the humidity-driven changes in swelling, mass uptake, and density of Nafion ionomer films cast at varying thicknesses (10–320 nm) onto a gold-plated sensor. The films were simultaneously probed during humidification using spectroscopic ellipsometry (SE) and a quartz crystal microbalance with dissipation (QCM-D), which allowed for determination of the density and shear stiffness. The effects of confinement were prominently observed below ∼30 nm, with films showing increased density along with decreased swelling and mass uptake during hydration. In addition, the confined films show a negative excess volume upon initial water sorption, implying a larger proportion of absorbed water might bound to ionic groups in accord with notion of localized densification.

Espinet, Kevin B. [University of California, Berke↗
DOE OSTI2024

Stabilization of Ni-YSZ Anodes in Solid Oxide Fuel Cells using an ALD-Grown Aluminum Titanate Interlayer

The effect of an Al 2 TiO 5 (ALT) interlayer between Ni and YSZ on enhancing the thermal stability of Ni-YSZ solid oxide fuel cell was examined. Atomic layer deposition (ALD) was used to provide precise control of the structure and thickness of the ALT interlayer. The study's findings demonstrate that a 2 nm thick ALT interlayer deposited by ALD does not adversely affect the cell's ohmic resistance and effectively prevents Ni sintering and the loss of active area during high-temperature heat treatments. ALT layers thicker than 2 nm, although they enhanced Ni stability, were found to impede oxygen ion transport in the electrode and significantly increase the ohmic resistance of the cell, leading to a decline in performance.

25 ENERGY STORAGE↗
DOE OSTI2023

Chromium Tolerant, Highly Active and Stable Electrocatalytic Internal Surface Coating for Cathode of Commercial SOFCs (Final Report)

This project is aimed to develop a chromium (Cr) tolerant, highly active, and stable coating layer on the internal surfaces of the porous composite cathode from commercially available SOFCs. Such coating layer was developed using the additive manufacturing process of Atomic Layer Deposition (ALD) and has been applied on the cathode consisting of either an electronic conductor of LaxSr 1-x MnyO 3-δ (LSM) or mixed ionic and electronic conducting La x Sr 1-x Co y Fe 1-y O 3-δ (LSCF). PI's work has demonstrated that the internal surface of cathode from the commercial cells, can be further tailored using ALD coating to dramatically enhance the cell performance. For instance, ALD layer consisting heterostructured nano composite of nano-Pt and nano-(Mn 0.8 Co 0.2 ) 3 O 4 oxide on the internal surface of porous LSM/YSZ cathode from SOFCs, has resulted in the large reduction of the cell polarizations resistance by up to 53%, and enormous increase of power density over 370%. For the cells with LSCF/Sm 2 O 3 doped CeO 2 (SDC) cathode, the conformal layer of nano-composite consisting of superjacent CoOx and subjacent minimum amount of Pt nano-grains has resulted in the power density enhancement by 126% for the large scale industry tubular cells at 750°C, and both the performance enhancement and nanostructure of the ALD layer are stable over ~ 2000 h continuous operation performed at industry test station. In the meanwhile, those ALD coating layer developed by PI's work is also inherently Cr-tolerant, and could act as physical barrier for preventing Cr diffusion into the cathode backbone, so as to mitigate the Cr poisoning effect on the cathode. In this project, the impact of Cr on the performance of those ALD coated commercial cells has been evaluated. Based on evolution of the cell performance, the ALD coating layer chemistry and ALD coating layer thickness has been optimized to maximize the overall Cr tolerance, cell power density and cell longevity. Different ALD coating has been applied onto the internal surface of LSM/YSZ and LSCF/SDC backbone respectively. The architecture/scaffold structures on the internal surface of different cathode, designed by this project, was catalogued and analyzed using High Resolution Transmission Electron Microscopy (HRTEM), and cell power/durability performance are assured via comprehensive electrochemical performance testing in the industry operation relevant conditions. The impact of the electrochemical operation current density, the water humidity, the cell operation temperature, and cell operation duration on the Cr tolerance of ALD coated cells has been systematically investigated. There is completely different nanostructure degradation mechanisms between LSM and LSCF cells induced by Cr contamination. For the LSCF/SDC baseline cell, With the Cr source, there is no apparent Sr surface segregation phase even for the baseline cell operated for 3000 h at 750 °C. With the Cr source, there is significant amorphous (SrCr)Ox phase accumulated in the original pore region. For the commercial baseline cells, Cr contaminants on the LSM electrode severely impacted the entire cell's electrochemical performance and nanostructure degradation. Those degradations include (1). Peak power density loss of 64 % after 109 h of operation. The dramatic increase in Rp (2). They are cracking at LSM/SSZ interface, LSM grains. SSZ remains intact but with (CrMn)Ox. By contrast, ALD coating (MnCo)Ox/Pt dramatically improves the Cr resistance, as follows (1). ALD-coated cell with a power density is 280-380 % of the baseline cell, depending on the ALD layer thickness. (2). For a cell with a 20 nm thick ALD layer, there is a large performance enhancement (> 200 % power density) induced by ALD coating of Cr-tolerant Mn 0.8 Co 0.2 Ox. (3). For a cell with a 20 nm thick ALD layer, after 168 h at 750 °C power density of the ALD-coated cell is ~ 600% of that baseline cell upon operation with Cr contamination for 109 h. The ALD coating on the internal surface of cathode developed by this project integrated multi-functions. Those multi-functions include (1). Dramatically improving the cell power density for the commercial cells; (2). Dramatically improving contamination resistance of the cathode, for being an excellent protection coating layer sealing off Cr contamination. (3). Dramatically increasing the cell longevity by potentially preventing the microstructure evolution and grain coarsening of the cathode. Overall, this project will provide a simple solution to simultaneously enhance power density and increase the reliability, robustness, and endurance of commercial SOFCs, over the entire operating temperature range of 650-800 °C. For the inherently functional SOFC, the ALD coating of LSM based cathode mitigate the Cr-contamination. Power density of ALD-coated cell is ~ 600% of that baseline cell upon operation with Cr contamination. In addition to SOFCs, the novel on-demand design approach and creation of multifunctional heterogeneous architecture on the electrode surface presented in this work opens further research for their application in other types of fuel cells, batteries, and sensors for which electrochemical reactions on the surface are similarly critical.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Understanding the Solution Dynamics and Binding of a PVDF Binder with Silicon, Graphite, and NMC Materials and the Influence on Cycling Performance

The impact of the binding, solution structure, and solution dynamics of poly(vinylidene fluoride) (PVDF) with silicon on its performance as compared to traditional graphite and Li 1.05 Ni 0.33 Mn 0.33 Co 0.33 O 2 (NMC) electrode materials was explored. Through refractive index (RI) measurements, the concentration of the binder adsorbed on the surface of electrode materials during electrode processing was determined to be less than half of the potentially available material resulting in excessive free binder in solution. Using ultrasmall-angle neutron scattering (USANS) and small-angle neutron scattering (SANS), it was found that PVDF forms a conformal coating over the entirety of the silicon particle. This is in direct contrast to graphite–PVDF and NMC–PVDF slurries, where PVDF only covers part of the graphite surface, and the PVDF chains make a network-like graphite–PVDF structure. Conversely, a thick layer of PVDF covers NMC particles, but the coating is porous, allowing for ion and electronic transport. The homogeneous coating of silicon breaks up percolation pathways, resulting in poor cycling performance of silicon materials as widely reported. These results indicate that the Si–PVDF interactions could be modified from a binder to a dispersant.

25 ENERGY STORAGE↗
DOE OSTI2021

Direct fabrication and characterization of vertically stacked Graphene/h-BN/Graphene tunnel junctions

We have used a lithography free technique for the direct fabrication of vertically stacked two-dimensional (2D) material-based tunnel junctions and characterized by Raman, AFM, XPS. We fabricated Graphene/h-BN/Graphene devices by direct deposition of graphene (bottom layer), h-BN (insulating barrier) and graphene (top layer) sequentially using a plasma enhanced chemical vapor deposition on Si/SiO 2 substrates. The thickness of the h-BN insulating layer was varied by tuning the plasma power and the deposition time. Samples were characterized by Raman, AFM, and XPS. The I-V data follows the barrier thickness dependent quantum tunneling behavior for equally doped graphene layers. The resonant tunneling behavior was observed at room temperature for oppositely doped graphene layers where hydrazine and ammonia were used for n-doping of one of the graphene layers. The resonance with negative differential conductance occurs when the band structures of the two electrodes are aligned. The doping effect of the resonant peak is observed for varying doping levels. The results are explained according to the Bardeen tunneling model.

2D-materials↗
DOE OSTI2025

Tip-based proximity ferroelectric switching and piezoelectric response in wurtzite multilayers

Proximity ferroelectricity is a paradigm for inducing ferroelectricity when a nonferroelectric polar material (such as Al⁢ N), which is unswitchable with an external field below the dielectric breakdown field, becomes a practically switchable ferroelectric in direct contact with a thin switchable ferroelectric layer (such as Al 1−𝑥 ⁢Sc 𝑥 ⁢N). Here, we develop a Landau-Ginzburg-Devonshire approach to study the proximity effect of local piezoelectric response and polarization reversal in wurtzite ferroelectric multilayers under a sharp electrically biased tip. Using finite-element modeling, we analyze the probe-induced nucleation of nanodomains, the features of local polarization hysteresis loops and coercive fields in the Al 1−𝑥 ⁢Sc 𝑥 ⁢N/Al⁢ N bilayers and three-layers. Similar to the wurtzite multilayers sandwiched between two parallel electrodes, the regimes of “proximity switching” (when all layers collectively switch) and the regime of “proximity suppression” (when they collectively do not switch) are the only two possible regimes in the probe-electrode geometry. However, the parameters and asymmetry of the local piezoresponse and polarization hysteresis loops depend significantly on the sequence of the layers with respect to the probe. The physical mechanism of proximity ferroelectricity in the local probe geometry is a depolarizing electric field determined by the polarization of the layers and their relative thickness. The field, whose direction is opposite to the polarization vector in the layer(s) with the larger spontaneous polarization (such as Al⁢ N), renormalizes the double-well ferroelectric potential to lower the steepness of the switching barrier in the “otherwise unswitchable” polar layers. Tip-based control of domains in otherwise nonferroelectric layers using proximity ferroelectricity can provide nanoscale control of domain reversal in memory, actuation, sensing, and optical applications. The ability of the tip-induced proximity switching to differentially switch multilayers, based on the order of the layers, provides a powerful tool for selective domain engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Stabilization of ferroelectric phase of Hf 0.6 Zr 0.4 O 2 on NbN and Nb [slides]

This work demonstrated both NbN and Nb make good electrodes for stabilizing orthorhombic phase of Hf 0.6 Zr 0.4 O 2 ferroelectric films. Wake up are < 100 cycles. P r can be as high as 30 µC/cm 2 - respectively 14 and 18 µC/cm 2 here. Further, capacitance suggests an orthorhombic phase can be stabilized. Addition of a linear dielectric under modest thickness can tune the P r and reduce leakage.

36 MATERIALS SCIENCE↗